Limit stop



R. STERRETT March 28, 1933.

LIMIT STOP Filed Feb'. 25, 1932 y lnveno': Y @055er SYTEEEETt far/:heya

Patented Mar. 28, 1933 UNITED STATES PATENT oI-I-lcE LIMIT sron Application led February 23, 1932. Serial No. 594,584.

This invention relates to limit stops, and more particularly to limit switches for use on cranes and similar hoisting devices.

Heretofore, limit switches of this class have generally been provided with two flexible members attached to an operating sheave or wheel and provided with counterweights which tend to maintain the switch in closed position. In the operation of the crane or other hoisting mechanism, one of the counterweights is adapted to be lifted so that the opposite counterweight will rotate the sheave or wheel and thereby open the limit switch. This form of mechanism is objectionable from the standpoint of safety, due

to the fact that the flexible members carrying the counterweights break at times, and the counterweights fall, endangering the lives of workmen below.v

The present invention provides a switch operating mechanism in which the likelihood of the counterweights dropping, due to broken cables or the like, is entirely eliminated.

In the drawing:

Figure 1 is a side elevation of a limit switch constructed in accordance with this invention and showing the switch in closed position.

Figure 2 is a similar view showing the switch in open position.

Referring more particularly to the drawing, the numeral 2 designates a limit switch, which may be of any standard construction, having a main operating shaft 3 of which is secured an actuating arm 4 having a counterweight 5 at one end. The switch 2 is secured to a base 6 which is, in turn, secured to any suitable portion of a crane or other hoisting 0 mechanism.

A rocking lever 7 is pivotally mounted intermediate its ends on the casing of the switch 2 and is provided with a counterweight 8 at one end, while its opposite end is connected by a cable or other flexible member 9 to an eye 10 adjacent the free end of a counterweighted lever 12, which is pivotally secured at one endV to a hanger 13 mounted on one of the frame members 14 of the hoisting mechanism. The lever 12 is provided with a counterweight 15 at its free end of suiicient weight to overcome the counterweight 8 of the lever 7. The arm 7 is provided with a pair of depending legs 17 and 18, one of which is positioned 011 each side of the pivoted pointof said arm. 'Ihe legs 17 and 18 are adapted to engage the end of the arm 4 opposite its counterweight 5 torotate the arm 4 and its shaft 3 when the rocking arm 7 moves about its pivotal mounting. 60'

The letter A designates the hoisting sheave block of the hoisting mechanism, which is provided with a bracket 16 adapted to engage and lift the lever 1 2 when the hoist block is raised to a predetermined position.

In operation, as the hoist sheave block A nears the upperlimit ofits travel the bracket 16 will engage the lever 12, lifting said lever upwardly against thefnormal pull of its counterweight 15 so as to release the lever 7 70 to the pull of its counterweight 8 and thereby cause the lever 7 to rotate about its pivotal mounting and force the depending leg 17 against the end of the arm 4 opposite the counterweight 5. p j I 75 This action rotates the arm 4 and shaft 3 until the counterweight 5 is moved beyond its center position, after which the counterweight 5 will fall by gravity to complete the rotative movement of the arm-4 and shaft 3 80 to open the limit switch. In order to reset the switch the hoist sheave block A will be lowered and the lever 12 will drop by gravity, thus pulling the arm 7 through the flexibe connection 9 against the counterweight 8 85 and forcing the depending leg 18 yagainst the end of the arm 4 opposite the counterweight 5 to rotate the arm 4 and shaft 3 until the counterweight 5 is moved beyond its center position, after which it will drop by gravity and complete the rotative movement of the shaft 3 to reset the switch 2.

llVhile I have .shown and described one specific form of my invention it will be understood that I do not wish to be limited thereto, since various modications may be made without. departing from the scope of my invention, as defined in the appended claims.

I claim:

1. The combination with a crane having a hoisting mechanism including a hoist sheave block, of a limit switch and means operated by said .sheave block for actuating said switch, said means comprising a counterweighted arm fixedly mounted intermediate its ends to an actuating shaft of said switch, a counterweighted rocking arm pivotally mounted on said switch at a point above said irst named arm, depending actuating legs carried by said rocking arm and adapted to engage the end of said first named arm opposite its counterweight whereby said rocking arm is moved about its pivotal mounting so as to lift said first named arm against its counterweight, and means normally tending to hold said rocking arm in one position against the pull of the counterweight of said arm, said means being actuated by the movement of said hoist sheave block to release said rocking arm to the pull of its counterweight.

2. rIlhe combination with a crane having a hoisting mechanism including a hoist sheave block, of a limit .switch and means operated by said sheave block for actuating said switch, said means comprising a counterweighted arm Xedly mounted intermediate its ends to an actuating shaft of said switch, a counterweighted rocking arm pivotally mounted on said switch at a point above said first named arm, depending actuating legs carried by said rocking arm and adapted to engage the end of said first named arm opposite its connterweight whereby said rocking arm is moved about its pivotal mounting so as to lift said rst named arm against its counterweight, a counterweighted lever supported at one end by the frame of .said crane and having its free counterweighted end connected to said rocking arm and being adapted to normally overcome the pull of the counterweight of said rocking arm, said lever being positioned in the path of travel of said hoist sheave block to release said rocking arm to the pull of its counterweight.

In testimony whereof, I have hereunto set my hand.

RCBERT STERRETT. 

